It's not true that Donald Trump was elected president because of Russian hacking, but it's also not true that the hacking never happened, Rep. Adam Kinzinger said Friday.

"The fact is, Congress and Americans need to find out what happened, to defend the Constitution," the Illinois Republican, a pilot in the Air National Guard, told Fox News' "America's Newsroom" program.

Any attempt to interfere with the integrity of United States elections need to be met with "swift punishment," Kinzinger continued, noting there have been many errors in U.S.-Russian policy, including with the situations in Ukraine and Syria.

"They are in eastern Ukraine, and [we] don't give offensive weapons to the Ukrainians," Kinzinger said. "This is Russia advancing until they hit a real read line, not a fake red line, and they haven't hit that yet."

He said he does have hope and is trying to be optimistic over Trump's call for re-engagement with Russia.

"It is one to say we want re-engagement," Kinzinger said. "That is fine. [President] George W. Bush did it, Barack Obama did it and integrated failure."

But it is one thing to call for a fresh look at the situation, but another to say the United States' role in the world must be maintained, Kinzinger said.

"The Russians have been advancing rather than retreating," Kinzinger said. "The good thing to keep in mind, [the hacking was] not an attempt to make Trump president by the Russians, but to undermine the faith in the Constitution. The Constitution is just a paper document until people agree, like we all do, that we will abide by those principles."